Technical Abstract:
Ruminants are considered a reservoir of E. coli O157:H7 but little is known about how animals become colonized. We developed a competitive colonization model in sheep to determine whether E. coli O157:H7 colonize ruminants more effectively than other pathotypes of E. coli. Six sheep were simultaneously inoculated with 10**10 or 10**7 CFU of 5 different strains of E. coli: 2 O157:H7, 2 enterotoxigenic (ETEC), and 1 enteropathogenic. At 2 days postinoculation (pi) all strains were detected in the feces of all animals. At 2 weeks pi 11/12 and 12/12 animals were still shedding the 2 O157:H7 strains but less than half of the animals were shedding the other 3 strains. At 2 months (m) the 2 strains of E. coli O157:H7 given at 10**10 CFU were detected in 2/6 and 4/6 animals at < or equal to 50 CFU/g. When these same strains were given at 10**7 CFU 2/6 animals were still shedding 2 m pi (< or equal to 100 CFU/g). This is in contrast to 1 ETEC strain which was shed (< or equal to 50 CFU/g) at 2 m pi by 3/6 animals given the 10**10 dose but 0/6 animals given the 10**7 dose. The other 2 strains were not detected at 2 m pi. These results indicate that E. coli O157:H7 may colonize the intestinal tract or ruminants more effectively than other pathotypes of E. coli.